A new fast Three Step Search motion estimation algorithm in H.264

SAD(Sum of Absolute Difference) is commonly used as the error estimate to identify the most similar block when trying to obtain the block motion vector in the process of motion estimation, which requires only easy calculation without the need for multiplication. Generally, the probability of the minimum SAD values is high when searching point is in the distance one pixel from the reference point. Thus, we reduced the searching area and then we can overcome the computational complexity problem. The main concept of proposed algorithm, which based on TSS(Three Step Search) method, first we find three minimum SAD points which is in integer distance unit, and then, in second step, the optimal point is in 1/2-pixel unit either between the most minimum SAD value point and the second minimum SAD point or between the most minimum SAD value point and the third minimum SAD point In third step, after finding the smallest SAD value between two SAD values on 1/2-pixel unit, the final optimized point is between the most minimum SAD value and the result value of the third step, in 1/2-pixel unit i.e., 1/4-pixel unit in totally. The conventional TSS method needs an eight search points in the sub-pixel steps in 1/2-pixel unit and also an eight search points in 1/4-pixel, to detect the optimal point, however the method suggested in this paper may detect only 5 search points.